Air data lateral-directional stability augmentation system

ABSTRACT

A system designed to augment lateral-directional stability of aircraft without the use of conventional gyroscopic sensing elements. A logic control system is used to interpret the dynamic pressure signals sensed near each wingtip, and the output of this logic can be used to provide actuation by pneumatic, electrical, or hydraulic actuations. Operation of both ailerons and rudder is normally involved, although aileron only control is possible in aircraft having inherently high directional damping.

States Patent AIR DATA LATERAL-DIRECTIONAL STABILITY AUGMENTATION SYSTEMDaniel 0. Dornmasch, Blawenburg, NJ.

The United States of America as represented by the Administrator of theFederal Aviation Administration Filed: Jan. 28, 1970 App]. No.: 6,636

Inventor:

Assignee:

us. 01. ..z3s/1so.2, 1 14/23, 244/315,

1m. 01. ..G06g 7/78 Field of Search 44/3.1s, 77 R; 235/1502; 73/180;114/23; 180/118; 318/580, 586, 589, 637, 645

References Cited UNITED STATES PATENTS 9/ 1 nqql f mfiji-z 31. 112:2:"

qL LEFT 5ENSOR 5EN5 -2 as 2 Wurmser ..l l4/23 Gerstine ..3 18/580 XPn'mary Examiner-Malcolm A. Morrison Assistant Examiner-R. StephenDildine, Jr. Attomey--Charles K. Wright, Jr., William G. Gapcynski andLawrence A. Neureither ABSTRACT Rub DER DISPLACEMENT S,- AcTu A10:

syar EM AIR DATA LATERAL-DIRECTIONAL STABILITY AUGMENTATION SYSTEMBACKGROUND OF THE INYENTION 1. Field of the Invention This invention isa lateral-directional stability augmentation system for aircraft whichuses sensed air datarather than gyroscopic or inertial sensors toprovide the basis for control of the ailerons and rudder.

2. Description of the Prior Art Earlier systems perfonningsimilarfunctions have been built using both rate and positiongyroscopes, and attempts have been made to use'raw air data to provideaileron control for "wings level" operation. These earlier air dataconcepts have not proven successful because of improper control lawlogic and because they lacked sufficient authority to overcome variablefriction in the control systems. Moreover, unless-rudder control as wellas aileron control is simultaneously used, roll stabilization based onlyon aileron operation will lead to unstable Dutch Roll oscillations inthe slow flight region of operation. This requires that the system beturned off below a given speed and altitude to ensure safe operation'ofthe aircraft.

The use of gyroscopic sensors on flexible aircraft poses major problemsin that the gyroscope sense the structural deformation modes, and unlesssteps are taken to prevent feedback of this information, couplingbetween the control logic and structural binding modes results.

SUMMARY OF THE INVENTION This invention provides lateral-directionalstabilization for an aircraft through the use of dynamic pressuresensors mounted near each wingtip, a control logic system, and anactuating system connected to the aircraft control surfaces throughclutch means so that the system may be manually overridden. Both theailerons and the rudder are controlled, thus preventing any tendencytoward oscillation in the slow flight region. The use of air datasensors, rather than gyroscopes, also eliminates the undesirablecoupling of the control system with he structural bending modes of theaircraft.

Therefore, it is an object of this invention to provide alateral-directional stabilization system for aircraft that is stableover all phases of flight operation and that does not couple withstructural bending modes of the aircraft.

It is a further object of this invention to provide a lateraldirectionalstabilization system for aircraft that is simple and inexpensive so thatit is applicable to general aviation aircraft.

It is also an object of this invention to provide a lateraldirectionalstabilizau'on system for aircraft which is capable of being manuallyoverridden at anytime.

BRIEF DESCRIPTION OF THE DRAWINGS The FIGURE is a functional blockdiagram of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the FIGURE, thereis shown a functional block diagram of the lateral-directionalstabilization system. The stabilization system is comprised of threebasic subgroups: the sensor elements, the control logic, and theactuator system. The sensor elements I, 2 are each pitot-static sensorsmounted near the wingtips of the aircraft. These sensors measure thedynamic pressure at the wingtips and provide an electrical signalindicative of the magnitude of thesensed qualities. The sensors shouldbe heated to prevent icing. The outputs from the right and left wingtipsare designated q,, and 4 respectively, and the sign of their difference,qrqk, is indicative of the direction of turn of the aircraft.

The logic system provides an output displacement command to the actuatorsystem in response to signals from the sensor elements. A logic systemwhich produces an actuation proportional to the error signal is said touse proportional logic. Proportional logic systems have the disadvantageof tending toward oscillatory instability at high gain values. They alsoinduce overshoot at even moderate. gains unless they are highly damped.Predictive or lead type logic, also known as error and error rate logic,features considerably improved high gain operation and total eliminationof error at moderate gain. In this type of logic both the error and itsrate of change are detected, and the probable error at some future timeis predicted. This predicted error is then used as the basis for thecontrol system.

The logic system generates'an output command to the actuator system bysolving the equation command where G is the system gain;

e, is the difi'erence in dynamic pressures, q, q

2,, is the sum of the dynamic pressures, q -l-q At is the predicted orlead time of the system; and

8 is the output command to the actuator system.

The dynamic pressure sensors 1, 2 provides signals q,, and q,,indicative of the dynamic pressures at the wingtips. These signals areconnected to unit 3 which forms the difference, e,,, between q and q,,and to unit 4 which determines the sum, 2,, of q,, and q The output 2,from 4 is connected to unit 5 which extracts the square root of E E.Unit 6 then operates Olly 2T, and e, to form the ratio 5W2; The signale, is differentiated by unit 7 and the predicted change at some futuretime, At, of the difference in dynamic pressure, e' At, is determined byunit 8. The predicted change in the dynamic pressure is added to thesignal e /Y; at node 9 to form the sum e IE $5M. This signal is' thenamplified by 1 amplifier ill l ito provide the output displacementcommand to the a ctuat ing system.

and a rudder actuator 12. Both the ailerons and the rudder are actuatedto prevent instability in the slow flight region of the aircraft. Theailerons are actuated by the output displacement command, and it isessential that this output be implemented as a rate rather than as atotal displacement command, since total displacement commands can leadto unstable behavior. The rudder is actuated proportionately to thedisplacement of the ailerons to counteract the effect of adverse aileronyaw. Fifty percent proportional rudder actuation has been found toinsure favorable characteristics in this embodiment; therefore, bymeasuring the total aileron displacement with a potentiometer or asynchro unit, the displacement command to the rudder actuator system canbe generated. Unit 13 provides an output command to the rudder actuatorsystem 12 according to the following relationship with the ailerondisplacement:

where 8,. is the rudder displacement, and

8., is the aileron displacement.

The actuator systems 11 and .12 are connected to their respectivecontrol surfaces through clutch means 14 and 15 so that thestabilization system can be manually overridden by the pilot. Thisparallel operation provides a unique safety feature as the pilot and thestabilization system are mutually redundant.

In normal operation any difference in the dynamic pressures sensed bysensors 1 and 2 will result in difference signal which will provide thebasis of an output displacement command to the actuator systems 11 and12. The resulting displacement of the control surfaces will tend toreturn the aircraft to a straight flight path. A heading bias signal efrom a VCR receiver could be applied to the control logic input toprovide for autopilot heading control and tracking functions, ifdesired.

I claim:

1. In an aircraft equipped with aileron and rudder control surfaces, alateral-directional stabilization system comprising a first dynamic airpressure sensor means which generates a first signal mounted near theright wingtip of said aircraft, a second dynamic air pressure sensormeans which generates a second signal mounted near the left wingtip ofsaid aircraft, means for combining said first and second signals to forman error signal, a logic system which produces an output displacementcommand being nonproportional to the error signal, actuating meansresponsive to said output displacement command to effect a displacementin said aileron and rudder control surfaces.

2. The system of claim 1 in which said actuating means comprises anaileron actuating system which actuates said aileron control surfaces ata rate responsive to said output displacement command and arudder-actuating system which causes a displacement of said ruddercontrol surface proportional to the displacement of said aileron controlsurfaces.

3. The system of claim 2 in which said rudder displacement is 50 percentof said aileron displacement.

4. The system of claim 1 in which said dynamic air pressure sensorelements are heated pitot-static sensors.

5. The system of claim 1 in which said actuator system is operativelyconverted to said aileron and rudder control surfaces through clutchmeans so that said stabilization system may be manually overridden.

6. In an aircraft equipped with aileron and rudder control surfaces, alateral-directional stabilization system comprising a first heatedpitot-static air pressure sensor means which generates a first signalmounted near the right wingtip of said aircraft, a second heatedpitot-static air pressure sensor means which generates a second signalmounted near the left wingtip of said aircraft, a logic systemcomprising means to combine said first and second signals to form asignal representative of the difi'erence between said first and secondsignals, means for combining said first and second signals to form asignal representative of the sum of said first and second signals,differentiating means responsive to said difference signal, means toform the product of said differentiated difference signal andincremental time to form a predicted pressure change signal, means forextracting the square root of said sum signal, combining means forforming a signal representative of the ratio of said difference signalto said square root of said sum signal, combining means for obtainingthe sum of said ratio signal and said predicted pressure change signalto form a third signal, amplifying means operating on said third signalto form an output displacement command signal, actuating meansresponsive to said output displacement command signal, said actuatingmeans comprising an aileron actuating signal which displaces saidaileron control surfaces at a rate responsive to said outputdisplacement command signal, and a rudder actuating system which causesa displacement of said rudder control surface proportional to thedisplacement of said aileron control surface, said actuating meansoperatively connected to said aileron and rudder control surfacesthrough clutch means so that said stabilization system may be manuallyoverridden.

1. In an aircraft equipped with aileron and rudder control surfaces, alateral-directional stabilization system comprising a first dynamic airpressure sensor means which generates a first signal mounted near theright wingtip of said aircraft, a second dynamic air pressure sensormeans which generates a second signal mounted near the left wingtip ofsaid aircraft, means for combining said first and second signals to forman error signal, a logic system which produces an output displacementcommand being nonproportional to the error signal, actuating meansresponsive to said output displacement command to effect a displacementin said aileron and rudder control surfaces.
 2. The system of claim 1 inwhich said actuating means comprises an aileron actuating system whichactuates said aileron control surfaces at a rate responsive to saidoutput displacement command and a rudder-actuating system which causes adisplacement of said rudder control surface proportional to thedisplacement of said aileron control surfaces.
 3. The system of claim 2in which said rudder displacement is 50 percent of said ailerondisplacement.
 4. The system of claim 1 in which said dynamic airpressure sensor elements are heated pitot-static sensors.
 5. The systemof claim 1 in which said actuator system is operatively converted tosaid aileron and rudder control surfaces through clutch means so thatsaid stabilization system may be manually overridden.
 6. In an aircraftequipped with aileron and rudder control surfaces, a lateral-directionalstabilization system comprising a first heated pitot-static air pressuresensor means which generates a first signal mounted near the rightwingtip of said aircraft, a second heated pitot-static air pressuresensor means which generates a second signal mounted near the leftwingtip of said aircraft, a logic system comprising means to combinesaid first and second signals to form a signal representative of thedifference between said first and second signals, means for combiningsaid first and second signals to form a signal representative of the sumof said first and second signals, differentiating means responsive tosaid difference signal, means to form the product of said differentiateddifference signal and incremental time to form a predicted pressurechange signal, means for extracting the square root of said sum signal,combining means for forming a signal representative of the ratio of saiddifference signal to said square root of said sum signal, combiningmeans for obtaining the sum of said ratio signal and said predictedpressure change signal to form a third signal, amplifying meansoperating on said third signal to form an output displacement commandsignal, actuating means responsive to said output displacement commandsignal, said actuating means comprisinG an aileron actuating signalwhich displaces said aileron control surfaces at a rate responsive tosaid output displacement command signal, and a rudder actuating systemwhich causes a displacement of said rudder control surface proportionalto the displacement of said aileron control surface, said actuatingmeans operatively connected to said aileron and rudder control surfacesthrough clutch means so that said stabilization system may be manuallyoverridden.